1. Field of the Invention
The present invention is generally directed to flow control valves and, more particularly, bi-propellant valves that control separate flows in substantially constant proportion over a range of flow rates.
2. Description of the Prior Art
Over the years, various types of flow control valves have been developed for rocket engine applications. Examples are shown in the brochure "Fox Venturi Valves" published by Fox Valve Development Company of East Hanover, N.J.
In valve applications such as bi-propellant valves for use in liquid rocket engines, it is very important that the flows occur in a substantially constant proportion. In the prior art, hydraulically or pneumatically actuated, pressure balanced throttling valves are often used for this purpose. "Fox Venturi Valves" shows one such valve wherein the propellant and oxidizer are introduced to the combustion chamber through two cavitating venturi ports. Two precision machined, needle-like pintles are located in respective throats of the cavitating venturi ports to provide respective annular orifices. The pintles are needle-shaped such that the size of the orifice is determined by the position of the pintles. The pintles are controlled by a servo valve that is driven in response to a command signal. By controlling the position of the pintles, the servo valve determines the sizes of the orifice in the venturi throat and, thus, the flow rate. The venturi throats are designed such that critical flow is maintained over a range of flow rates. Thus, the venturi ports continuously provide throttled liquids over the range of flow rates.
Typically, in rocket applications, the servo valve is powered by internal line pressure from liquid fuel on-board the rocket. This avoids the need for hydraulics or large on-board power supply systems. However, this system also has several disadvantages. It is inefficient in that fuel that is vented to adjust the position of the valve, together with quiescent leakage of the servo valve, is merely dumped overboard. Also, manufacture of the pintles required high precision machining and matching as well as high surface finishes. The necessary contours, surface areas and finishes of the pintles are difficult to attain and to reliably reproduce.
Accordingly, there was a need in the prior art for a bi-propellant flow control valve that was more fuel efficient and that was simpler and less difficult to manufacture.